Reprint from THE "HOW-TO-DO-IT" BOOKS

PRACTICAL MECHANICS FOR BOYS
By J. S. ZERBE, M.E.

A book which treats, in a most practical and fascinating manner all subjects pertaining to the "King of Trades"; showing the care and use of tools; drawing; designing, and the laying out of work; the principles involved in the building of various kinds of structures, and the rudiments of architecture. It contains over two hundred and fifty illustrations made especially for this work, and includes also a complete glossary of the technical terms used in the art. The most comprehensive volume on this subject ever published for boys.

Copyright, 1914, by
THE NEW YORK BOOK COMPANY

Publisher's disclaimer: Content provided is dated and is for information purposes only.

I - II - III - IV - V - VI - VII - VIII - IX - X - XI - XII - XIII - XIV - XV - XVI - XVII

PRACTICAL MECHANICS FOR BOYS

CHAPTER VI

ILLUSTRATING SOME OF THE FUNDAMENTAL DEVICES

There are numerous little devices and shop expedients which are desirable, and for which the boy will find uses as he progresses.

We devote this chapter to hints of this kind, all of which are capable of being turned out or utilized at various stages.

Figs. 58.-61. Belt Lacing

Lacing Belts.—To properly lace a belt is quite an art, as many who have tried it know. If a belt runs off the pulley it is attributable to one of three causes: either the pulleys are out of line or the shafts are not parallel or the belt is laced so it makes the belt longer at one margin than the other.

In Fig. 58 the lacing should commence at the center hole (A) of one belt end and lace outwardly, terminating at the hole (B) in the center of the other belt end, as shown in Fig. 58.

In Fig. 59 the lacing commences at A, and terminates at the hole (B) at the edge. This will be ample for all but the widest belts.

Fig. 60 is adapted for a narrow belt. The lacing commences at one margin hole (A), and terminates at the other margin hole (Z)

Fig. 61 shows the outside of the belt.

Fig. 62. Bevel Gears Fig. 63. Miter Gears Fig. 64. Crown Wheel Fig. 65. Grooved Friction Gears Fig. 66. Valve Fig. 67. Cone Pulleys Fig. 68. Universal Joint

Fig. 62. Gears.—This is something every boy ought to know about. Fig. 62 shows a pair of intermeshing bevel gears. This is the correct term for a pair when both are of the same diameter.

Miter Gears.—In Fig. 63 we have a pair of miter gears, one being larger than the other. Remember this distinction.

Fig. 64. Crown Wheel.—This is a simple manner of transmitting motion from one shaft to another, when the shafts are at right angles, or nearly so, without using bevel or miter gears.

Fig. 65. Grooved Friction Gearing.—Two grooved pulleys, which fit each other accurately, will transmit power without losing too much by friction. The deeper the grooves the greater is the loss by friction.

Fig. 66. A Valve Which Closes by the Water Pressure.—The bibb has therein a movable valve on a horizontal stem, the valve being on the inside of the seat. The stem of the handle has at its lower end a crank bend, which engages with the outer end of the valve stem. When the handle is turned in either direction the valve is unseated. On releasing the handle the pressure of the water against the valve seats it.

Fig. 67. Cone Pulleys.—Two cone pulleys of equal size and taper provide a means whereby a change in speed can be transmitted from one shaft to another by merely moving the belt to and fro. The slightest change is available by this means.

Fig. 68. Universal Joint.—A wheel, with four projecting pins, is placed between the U-shaped yokes on the ends of the approaching shafts. The pins serve as the pivots for the angles formed by the two shafts.

Fig. 69. Trammel Fig. 70. Escapement Fig. 71. Device for Holding Wheel Fig. 72. Rack and Pinion Fig. 73. Mutilated Gears Fig. 74. Shaft Coupling

Fig. 69. Trammel for Making an Ellipse.—This is a tool easily made, which will be of great service in the shop. In a disc (A), preferably made of brass, are two channels (B) at right angles to each other. The grooves are undercut, so that the blocks (C) will fit and slide in the grooves and be held therein by the dove-tailed formation. Each block is longer than the width of the groove, and has an outwardly projecting pin which passes through a bar (D). One pin (E) is movable along in a slot, but is adjustable at any point so that the shape of the ellipse may be varied. The end of the bar has a series of holes (G) for a pencil, so that the size of the ellipse may also be changed.

Fig. 70. Escapements.—Various forms of escapements may be made, but the object of all is the same. The device is designed to permit a wheel to move intermittingly or in a step by step movement, by the swinging motion of a pendulum. Another thing is accomplished by it. The teeth of the escapement are cut at such an angle that, as one of the teeth of the escapement is released from one tooth of the escapement wheel, the spring, or the weight of the clock, will cause one of the teeth of the escapement wheel to engage the other tooth of the escapement, and give the pendulum an impulse in the other direction. In the figure, A is the escapement, B the escapement wheels and a, b, the pallets, which are cut at suitable angles to actuate the pendulum.

Fig. 71. Simple Device to Prevent a Wheel or Shaft prom Turning Back.—This is a substitute for a pawl and ratchet wheel. A is a drum or a hollow wheel and B a pulley on a shaft, and this pulley turns loosely with the drum (A). Four tangential slots (C) are cut into the perimeter of the pulley (B), and in each is a hardened steel roller (D). It matters not in what position the wheel (B) may be, at least two of the rollers will always be in contact with the inside of the drum (A), and thus cause the pulley and drum to turn together. On reversing the direction of the pulley the rollers are immediately freed from binding contact.

Fig. 72. Racks and Pinions.—The object of this form of mechanism is to provide a reciprocating, or back-and-forth motion, from a shaft which turns continually in one direction. A is the rack and B a mutilated gear. When the gear turns it moves the rack in one direction, because the teeth of the gear engage the lower rack teeth, and when the rack has moved to the end its teeth engage the teeth of the upper rack, thus reversing the movement of the rack.

Fig. 73. Mutilated Gears.—These are made in so many forms, and adapted for such a variety of purposes, that we merely give a few samples to show what is meant by the term.

Fig. 74. Simple Shaft Coupling.—Prepare two similarly formed discs (A, B), which are provided with hubs so they may be keyed to the ends of the respective shafts. One disc has four or more projecting pins (C), and the other disc suitable holes (D) to receive the pins.

Fig. 75. Clutches Fig. 76. Ball and Socket Joints Fig. 77. Fastening Ball Fig. 78. Tripping Devices Fig. 79. Anchor Bolt Fig. 80. Lazy Tongs. Fig. 81. Disc Shears.

Fig. 75. Clutches.—This is a piece of mechanism which is required in so many kinds of machinery, that we show several of the most approved types.

Fig. 76. Ball and Socket Joints.—The most practical form of ball and socket joints is simply a head in which is a bowl-shaped cavity the depth of one-half of the ball. A plate with a central opening small enough to hold in the ball, and still large enough at the neck to permit the arm carrying the ball to swing a limited distance, is secured by threads, or by bolts, to the head. The first figure shows this.

Fig. 77 illustrates a simple manner of tightening the ball so as to hold the standard in any desired position.

Fig. 78. Tripping Devices.—These are usually in the form of hooks, so arranged that a slight pull on the tripping lever will cause the suspended articles to drop.

Fig. 79. Anchor Bolt.—These are used in brick or cement walls. The bolt itself screws into a sleeve which is split, and draws a wedge nut up to the split end of the sleeve. As a result the split sleeve opens or spreads out and binds against the wall sufficiently to prevent the bolt from being withdrawn.

Fig. 80. Lazy Tongs.—One of the simplest and most effective instruments for carrying ice, boxes or heavy objects, which are bulky or inconvenient to carry. It grasps the article firmly, and the heavier the weight the tighter is its grasp.

Fig. 81. Disc Shears.—This is a useful tool either for cutting tin or paper, pasteboard and the like. It will cut by the act of drawing the material through it, but if power is applied to one or to both of the shafts the work is much facilitated, particularly in thick or hard material.

Fig. 82. Wabble Saw Fig. 83. Continuous Crank Motion Fig. 84. Continuous Feed Fig. 85. Crank Motion Fig. 86. Ratchet Head Fig. 87. Bench Clamp

Fig. 82. Wabble Saw.—This is a most simple and useful tool, as it will readily and quickly saw out a groove so that it is undercut. The saw is put on the mandrel at an angle, as will be seen, and should be run at a high rate of speed.

Fig. 83. Crank Motion by a Slotted Yoke.—This produces a straight back-and-forth movement from the circular motion of a wheel or crank. It entirely dispenses with a pitman rod, and it enables the machine, or the part of the machine operated, to be placed close to the crank.

Fig. 84. Continuous Feed by the Motion of a Lever.—The simple lever with a pawl on each side of the fulcrum is the most effective means to make a continuous feed by the simple movement of a lever. The form shown is capable of many modifications, and it can be easily adapted for any particular work desired.

Fig. 85. Crank Motion.—By the structure shown, namely, a slotted lever (A), a quick return can be made with the lever. B indicates the fulcrum.

Fig. 86. Ratchet Head.—This shows a well-known form for common ratchet. It has the advantage that the radially movable plugs (A) are tangentially disposed, and rest against walls (B) eccentrically disposed, and are, therefore, in such a position that they easily slide over the inclines.

Fig. 87. Bench Clamp.—A pair of dogs (A, B), with the ends bent toward each other, and pivoted midway between the ends to the bench in such a position that the board (C), to be held between them, on striking the rear ends of the dogs, will force the forward ends together, and thus clamp it firmly for planing or other purposes.

Fig. 88. Helico-Volute Spring Fig. 89. Double Helico-Volute Fig. 90. Helical Spring Fig. 91. Single Volute Helix-Spring Fig. 92. Flat Spiral or Convolute Fig. 93. Eccentric Rod and Strap Fig. 94. Anti-Dead Center for Foot-Lathes

Fig. 88. Helico-Volute Spring.—This is a form of spring for tension purposes. The enlarged cross-section of the coil in its middle portion, with the ends tapering down to the eyes, provides a means whereby the pull is transferred from the smaller to the larger portions, without producing a great breaking strain near the ends.

Fig. 89. Double Helico-Volute.—This form, so far as the outlines are considered, is the opposite of Fig. 88. A compression spring of this kind has a very wide range of movement.

Fig. 90. Helical Spring.—This form of coil, uniform from end to end, is usually made of metal which is square in cross-section, and used where it is required for heavy purposes

Fig. 91. Single Volute Helix-Spring.—This is also used for compression, intended where tremendous weights or resistances are to be overcome, and when the range of movement is small.

Fig. 92. Flat Spiral, or Convolute.—This is for small machines. It is the familiar form used in watches owing to its delicate structure, and it is admirably adapted to yield to the rocking motion of an arbor.

Fig. 93. Eccentric Rod and Strap.—A simple and convenient form of structure, intended to furnish a reciprocating motion where a crank is not available. An illustration of its use is shown on certain types of steam engine to operate the valves.

Fig. 94. Anti-Dead Center for Foot-Lathes.—A flat, spiral spring (A), with its coiled end attached to firm support (B), has its other end pivotally attached to the crank-pin (C), the tension of the spring being such that when the lathe stops the crack-pin will always be at one side of the dead-center, thus enabling the operator to start the machine by merely pressing the foot downwardly on the treadle (D).


To Chapter VII - Properties of Materials

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